[ruby-core:107989] [Ruby master Bug#18641] UTF-16 surrogate pairs

Issue #18641 has been updated by noraj (Alexandre ZANNI).


Thank you Martin.

I'm actually working on an Unicode study, I was not interested into representing the emoji with it's codepoint but to actually be able to write non-BMP glyph in UTF-16 by using the surrogates.

As far as I understand, it's not possible to have a native UTF-16 string it will always be UTF-8 converted to UTF-16 so my only option to write surrogates directly is to use pack?

----------------------------------------
Bug #18641: UTF-16 surrogate pairs
https://bugs.ruby-lang.org/issues/18641#change-96942

* Author: noraj (Alexandre ZANNI)
* Status: Rejected
* Priority: Normal
* ruby -v: ruby 3.1.1p18 (2022-02-18 revision 53f5fc4236) [x86_64-linux]
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
That Ruby triggers an *invalid Unicode codepoint* error while using surrogate pairs in an UTF-8 string is expected, however those codepoints should be valid in an UTF-16 string.
It is also expected that unpaired surrogates are invalid however paired surrogates are valid cf. https://unicode.org/faq/utf_bom.html#utf16-7.

Version tested: 3.0.3p157, 3.1.0p0 and 3.1.1p18

``` ruby
➜ irb
irb(main):001:0> a = ''.force_encoding(Encoding::UTF_16)
=> ""
irb(main):002:0> a += "\uD83D\uDC69".force_encoding(Encoding::UTF_16)
/home/noraj/.asdf/installs/ruby/3.1.0/lib/ruby/3.1.0/irb/workspace.rb:119:in `eval': (irb):2: invalid Unicode codepoint (SyntaxError)                                                                            
a += "\uD83D\uDC69".force_encoding(Encodi...                                                
        ^~~~                                                                                
(irb):2: invalid Unicode codepoint                                                          
a += "\uD83D\uDC69".force_encoding(Encoding::UT...                                          
              ^~~~                                                                          
        from /home/noraj/.asdf/installs/ruby/3.1.0/lib/ruby/gems/3.1.0/gems/irb-1.4.1/exe/irb:11:in `<top (required)>'                                                                                           
        from /home/noraj/.asdf/installs/ruby/3.1.0/bin/irb:25:in `load'                     
        from /home/noraj/.asdf/installs/ruby/3.1.0/bin/irb:25:in `<main>'
```

Also see [Unicode 14.0 Implementation Guidelines - 5.4 Handling Surrogate Pairs in UTF-16](https://www.unicode.org/versions/Unicode14.0.0/ch05.pdf)



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